The clutch actuator for manual transmission motor vehicles comprises a selectively displacable element which is connected to the release element of the clutch assembly to separate two rotatable elements of the clutch, which elements are normally frictionally coupled to transfer energy from the engine crank shaft to the transmission input shaft. In the case of a hydraulic actuator, the actuator comprises the slave portion of a hydraulic master cylinder/slave cylinder assembly wherein the master cylinder is mounted to be directly operated by the clutch pedal.
As is well known, the release element of the clutch rotates at engine speed when the clutch is engaged and slows down and may eventually stop when the clutch is released or disengaged to permit a gear change. The actuator on the other hand is nonrotating, that is, the body of the actuator must be secured against rotation to a structural component such as a transmission housing or the clutch housing. Therefore, the clutch actuator must be connected to the release element through a bearing commonly called a throw out or a release bearing.
The actuator can be mounted off axis or externally relative to the transmission input shaft or it can be mounted concentrically. The off axis or external arrangement involves a lever arm connected between the actuator output element and the clutch release member. The typical concentric arrangement requires no such lever arm. Instead, the cylinder body of the actuator is fixed to the clutch bell housing or to the face of the transmission housing and the axially translatable piston is connected to the outer race of the throw out bearing. The inner race is in turn connected to the clutch release element. Examples of concentric actuator arrangements are shown for example in U.S. Pat. Nos. 4,585,106; 4,585,107; 4,585,108, 4,585,109; 4,609,087; 4,624,290; 4,660,694; 4,684,003; 4,687,084 and 4,708,228 all assigned to the assignee of the present invention.
Whereas these prior art concentric actuators are satisfactory in most applications, there are certain applications where the size and/or profile of the prior art actuators present problems with respect to installation and/or operation.